A big part of the problem on the early models (besides too much oil) was that Yamaha made the breather outlets too big. Through the '70s, they tried several "fixes". First one was to cap one outlet off completely and only use the other one. Next try was going back to the 2 outlets but with rubber reducer plugs fitted into them. Finally, they redesigned the breather housing, changing it to a single outlet with a very small hole in it. You can retrofit this late style single pipe breather housing to your early bike if you like.